The European perspective on nitrogen emission and deposition.

Europe has been successful in reducing the emissions of several nitrogenous pollutants over recent decades. This is reflected in concentrations and deposition rates that have decreased for several components. Emissions of nitrogen containing gases are estimated to have decreased in Europe by 10%, 21% and 14% for N(2)O, NO(x) and NH(3), respectively, between 1990 and 1998. The main reductions are the result of a decrease in industrial and agricultural activities in the east of Europe. The reductions are a result of the economic situation, measures in the transport sector, industry, and the agricultural sector, with only a small part of the reduction due to specific measures designed to reduce emissions. The reduction is significant but far from the end goal for large areas in Europe, in relation to different environmental problems. The Gothenburg Protocol will lead to reductions of 50% and 12% in 2010 relative to 1990 for NO(x) and NH(3), respectively. The N(2)O emissions are expected to grow by 9% between 1998 and 2010. Further reductions are necessary to reach critical limits for ecosystem protection, air quality standards, and climate change. Emissions of nitrogen compounds result from an overload of reactive nitrogen that is produced by combustion processes, by synthesis of ammonia, or by import from other areas as concentrated animal feeds. Some improvements can be made in the efficiency of combustion processes and agricultural systems. However, measures to reduce emissions substantially need to focus on decreasing the production or import of reactive N. Reactive N ceilings for regions, based on critical limits for all N-related effects, can help to focus such measures. An integrated approach might have advantages over the pollutant-specific approach, to combat nitrogen pollution. This could provide the future direction for European policy to reduce the impacts of excess nitrogen.